This invention relates to devices for the treatment of heart disease and particularly to endo-arterial prosthesis, which are commonly called stents. More particularly, the invention relates to a stent delivery system having an adjustable length balloon catheter for interventional treatment of diseased vessels.
Several interventional treatment modalities are presently used for heart disease including balloon and laser angioplasty, atherectomy and by-pass surgery. In typical balloon angioplasty procedures, a guiding catheter having a performed distal tip is percutaneously introduced through the femoral artery into the cardiovascular system of a patient in a conventional Seldinger technique and advanced within the cardiovascular system until the distal tip of the guiding catheter is seated in the ostium. A guidewire is positioned within an inner lumen of a dilatation catheter and then both are advanced through the guiding catheter to the distal end thereof. The guidewire is first advanced out of the distal end of the guiding catheter into the patient's coronary vasculature until the distal end of the guidewire crosses a lesion to be dilated, then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient's coronary anatomy over the previously introduced guidewire until the balloon of the dilatation catheter is properly positioned across the lesion. Once in position across the lesion, the balloon, which is made of relatively inelastic materials, is inflated to a predetermined size with radiopaque liquid  at relatively high pressure (e.g., greater than four atmospheres) to compress the arteriosclerotic plaque of the lesion against the inside of the artery wall and to otherwise expand the inner lumen of the artery. The balloon is then deflated so that blood flow can be resumed through the dilated artery and the dilatation catheter can be removed therefrom.
One problem which can occur during balloon angioplasty procedures is the formation of intimal flaps which can collapse and occlude the artery when the balloon is deflated at the end of the angioplasty procedure. Another problem characteristic of balloon angioplasty procedures is the large number of patients which are subject to restenosis in the treated artery. In the case of restenosis, the treated artery may again be subjected to balloon angioplasty or to other treatments such as by-pass surgery, if additional balloon angioplasty procedures are not warranted. However, in the event of a partial or total occlusion of a coronary artery by the collapse of a dissected arterial lining after the balloon is deflated, the patient may require immediate medical attention, particularly in the coronary arteries.
Much development work in the treatment of heart disease has been directed to stents. Stents are generally cylindrically shaped intravascular devices which are placed within an artery to hold it open. The device can be used to prevent restenosis and to maintain the patency of a blood vessel immediately after intravascular treatments. In some circumstances, they can also be used as the primary treatment device where they are expanded to dilate a stenosis and then left in place.
One prior art method and system developed for delivering stents to  desired locations within the patient's body lumen involves crimping a stent about an expandable member, such as a balloon on the distal end of a catheter, advancing the catheter through the patient's vascular system until the stent is in the desired location within a blood vessel, and then inflating the expandable member on the catheter to expand the stent within the blood vessel. The expandable member is then deflated and the catheter withdrawn, leaving the expanded stent within the blood vessel, holding open the passageway thereof.
Generally, a stent requires an expandable member to be at least as long as the stent in order to fully expand the stent. Once the stent is deployed, it is sometimes necessary to post dilate certain areas of the stent at high pressure to more fully open the most constricted areas. If the expandable member is longer than the stent, the post dilation will also dilate unstented regions at the stent ends. This is undesirable as it can create edge dissections or increased restenosis. It is desirable to have the post dilation expandable member to be somewhat shorter than the delivery/deployment expandable member. One means of achieving this is to exchange the delivery system expandable member for a separate but shorter dilatation expandable member. However, this increases the procedure time and costs.
Some prior art stent delivery systems for implanting balloon expandable stents also utilize an outer delivery sheath which is initially placed over the compressed stent prior to deployment. A delivery sheath is sometimes needed to prevent the stent from moving axially along the balloon portion of the delivery catheter while being deployed into the patient's vasculature. Additionally, sometimes  the stent cannot be deployed for a variety of reasons. In those instances, the stent must be able to be pulled back into the guiding catheter without being “stripped off” of the delivery catheter. Thus, the outer sheath remains in place over the compressed stent until the physician has manipulated the catheter into the proper location in the patient's vasculature. Thereafter, once in place, the physician can retract the outer sheath to expose the stent within the body vessel. The physician then can inflate the balloon portion of the dilatation catheter to cause the compressed stent to expand to a larger diameter to be left in place within the body vessel at the target site. Despite the care given during handling, stents can become dislodged from the delivery system. The consequences of losing a stent can range from embarrassment to a life-threatening situation that requires immediate surgery.
This outer delivery sheath also helps prevent the stent from abraiding the vessel wall as it is being delivered through the vasculature into the target area. Otherwise, the struts of the stent would be exposed to the vessel walls of the patient's vasculature and could possibly cause trauma to the walls or could cause pieces of plaque to break off from a stenosis as the delivery system is being positioned across a tight stenosis. Abrasive forces in the area of a stenosis are not desirable due to the possible formation of embolic debris which could be released into the patient's blood stream. Such debris could possibly occlude smaller blood vessels leading to vital organs, such as the brain.
What has been needed and heretofore unavailable is a stent delivery device, which allows for a variable length expandable member needed for proper stent  deployment and safe and effective post dilation of a deployed stent. Also, the stent delivery device should be capable of increasing stent security by preventing the stent from moving axially along the balloon portion of the delivery catheter and should prevent the stent from abraiding the vessel wall as it is being delivered through the patient's vasculature. The present invention satisfies these and other needs.